On Tuesday, voters in three Colorado cities, including this college town about an hour north of Denver and nearby Lafayette and Boulder, passed initiatives against fracking, a drilling technique key to extracting oil and natural gas around the country but controversial for its environmental and health risks. A similar measure in the town of Broomfield failed by an extremely narrow margin, and it's likely to face an automatic recount. Three Ohio cities also voted on anti-fracking measures. Two, Bowling Green and Youngstown, defeated the initiatives, while another, Oberlin, passed it. It's likely that anti-fracking activists in Colorado will seek a statewide ban on fracking in next year's election.

Fracking, formally known as hydraulic fracturing, involves injecting chemicals and large amounts of water and sand miles underground to unlock oil and natural gas trapped in shale formations in places like North Dakota, Pennsylvania, and here in Colorado. Nearly 90 percent of new wells in Colorado are fracked, according to the state's Department of Natural Resources.

This technology, combined with horizontal drilling, is revolutionizing America's energy landscape and reinvigorating the economy. It's also igniting fights about a range of public health and environmental concerns.

What are the biggest issues driving opposition to fracking? What more can both the oil and natural-gas industry and environmental and health organizations do to ensure these concerns are adequately addressed?

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How, if at all, does the national fight over global warming intersect with local worries about air quality and water contamination?